Devices based upon the nonlinear optical properties of materials are known in the art. Such devices include electrooptical modulators and switches, frequency converters, frequency doublers, optical mixers, optical parametric oscillators and amplifiers, directional couplers and data processors. Typically, these devices have utilized as the optically nonlinear media inorganic crystals, such as LiNbO.sub.3, organic materials, such as 2-methyl-4-nitroaniline, and poled polymers containing dipolar dye moieties. However, due to the difficulties in preparing uniform, stable and properly oriented films of such materials for use in integrated devices, an effort has been directed recently to organic multilayer thin films as the active media in second-order nonlinear optical devices. The use of such films would be highly advantageous because organic composites can exhibit nonlinear susceptibilities equaling or exceeding those of such inorganic materials as lithium niobate and could be deposited on various substrates from liquid solutions.
Jacob Sagiv and co-workers proposed formation of multilayer films by a "self-assembly" strategy, which is based on repeated formation of monolayers by the irreversible chemisorption of molecules from homogeneous solutions. See Lucy Netzer et al., "Absorbed Monolayers versus Langmuir-Blodget Monolayers--Why and How? II: Characterization of Built-Up Films Constructed by Stepwise Absorption of Individual Monolayers", Thin Solid Films, Vol. 106 (1983), pp. 67-76; Lucy Netzer and Jacob Sagiv, "A New Approach to Construction of Artificial Monolayer Assemblies", Journal of the American Chemical Society, Vol. 105, 1983, pp. 674-676; and Rivka Maoz et al., "Self-Assembling Monolayers in the Construction of Planned Supermolecular Structure and as Modifiers of Surface Properties", Journal de Chemie Physique, Vol. 85, No. 11/12, 1988, pp. 1059-1065. To assure layer-by-layer deposition, the chemisorption process is designed to be self-limiting at one monolayer, and a subsequent chemical treatment is used to reactivate the surface for chemisorption of the next monolayer. However, while Sagiv and co-workers used the self-assembly procedure for formation of monolayers into multilayer assemblies, the process was not suited for facile preparation of properly functionalized organic multilayer films with polar orientation. DeQuan Li et al. suggested self-assembly of organic multilayers into nonlinear optical thin films. Li et al. modified the self-assembly technology of Sagiv by introducing soft polymeric layers transverse to the stacking direction of the monolayers. See DeQuan Li, "Chromophoric Self-Assembled Multilayers, Organic Superlattice Approaches to Thin Film Non-Linear Optical Materials", Journal of the American Chemical Society, Vol. 112, No. 20, 1990, pp. 7389-7390. However, this procedure suffered from a cumbersome process and included much material that is not optically active.
It would be useful to develop alternative methods for depositing organic multilayers using simple chemical processes to form films containing a large volume fraction of optically nonlinear materials, with a high degree of polar orientation and stability.